Stacking apparatus for wood veneer and other sheet material

ABSTRACT

Disclosed herein is an apparatus for evenly stacking sheet material and particularly for evenly laying-up core and face sheets of wood veneer for making plywood of various thicknesses. The apparatus includes a substantially rectangular frame on which is mounted a barrier plate serving as a straight edge to align the lead edge of the veneer sheets delivered into a stacking position overlying a receiving surface, generally a conventional scissors hoist or lift. A series of spaced-apart clamping fingers project through the barrier plate, the fingers functioning to grasp and hold the lead edge of veneer delivered into engagement with them by a variable speed reciprocating conveyor. The reciprocating conveyor, after delivering the veneer to stacking position, is withdrawn from beneath the wood veneer a distance greater than the width of the veneer, thereby allowing the trailing edge of the veneer to fall to the top of the receiving surface. At substantially the same time suitable control means effect withdrawal of the clamping means to release the lead edge of the veneer held by the clamping means allowing the lead edge to fall to the top of the receiving surface.

United States Patent [72] Inventors Victor H. Clausen Bellevue; James E. Rasmussen, Seattle, Wash. [21] Appl.No. 793,022 1 [22] Filed Jau.22, 1969 [45] Patented Mar.2, 1971 [73] Assignee Simpson Timber Company Seattle,Wash.

[5 4] STACKING APPARATUS FOR WOOD VENEER AND OTHER SHEET MATERIAL 8 Claims, 5 Drawing Figs.

[52] (1.8.01 214/6, 198/l10,271/68 [51] Int.Cl ..B65g57/l0 [50] FieldofSearch ....214/6(P),6 (10,6 (G),6 (H); 271/86, 88,68, 84, 69; 198/110 [56] References Cited UNITED STATES PATENTS 1,270,334 6/1918 Schumacher.... 271/84 2,413,979 1/1947 Lamb 214/6(l-l) 2,549,202 4/1951 ldelman.... 214/6(l() .3,028,979 4/1962 Zachow.... 214/6(K) 3,143,222 8/1964 Caskie 214/6(P) 3,247,981 4/1966 Johnson... 214/6(P) 3,281,146 10/1966 Bridge 214/6(l()UX 3,239,815 12/1966 Richter et a]. 214/6(K)X 3,405,932 10/1968 Dame 271/84X 3,410,423 11/1968 Brockmuller...v 2l4/6(K) 3,411,638 11/1963 Dryon 2l4/6(K) Primary Examiner-Gerald M. Forlenza Assistant Examiner-Robert J. Spar Attorney-Seed, Berry and Dowrey ABSTRACT: Disclosed herein is an apparatus for evenly stacking sheet material and particularly for evenly laying-up core and face sheets of wood veneer for making plywood of various thicknesses. The apparatus includes a substantially width of the veneer, thereby allowing; the trailing edge of the veneer to fall to the top of the receiving surface. At substantially the same time suitable control means effect withdrawal of the clamping means to release the lead edge of the veneer held by the clamping means allowing the lead edge to fall to the top of the receiving surface.

ew-m 2m 3567.047

gum 2 OF 3 FIG-2 JAMES E. RASMUSSEN VICTOR H. CLAUSEN V INVENTOR.

ATTORNEYS PATENTEUHAR 21971 3567041 sums [1F 3 JAMES E. RASMUSSEN VICTOR H. (BLAUSEN INVENTQR.

ATTORNEYS STACKING APPARATUS FOR WOOD VENEER AND OTHER SHEET MATERIAL BACKGROUND OF THE INVENTION apparatus for sheet tioned patent as well asother available equipment is not capable of maintaining an uninterrupted flow of veneer sheets to the stacking station and stacking the veneer sheets evenlyas is the apparatus of this invention.

SUMMARY OF THE INVENTION I This invention relates to an apparatus for evenly stacking sheet material, particularly wood;: veneer. I A rapidly reciprocating, conveyor is used to convey the sheet material from a delivery position to a forwardpositionroverlying a receiving surface where the material is to be stacked. Abarrier plate or backstop is positioned above and adjacent towthe receivingsurface and forms an aligning surface for the lead edge of the sheet material delivered into contact therewith by the reciprocating conveyor. Projecting through the barrier plate at spaced intervals are. a series of clamping means at subst antially the s ame level as the top: surface of the reciprocating conveyor, the clampingmeans functioningtoengage and hold the lead edge of the sheet material. fed thereto by. the reciprocating conveyor. In operation, sheet material is delivered to the top surface ofthe reciprocatingconveyor. The reciprocating conveyor conveys the sheet material from thedelivery position to a position overlying the receivingisurface where the lead edge of the sheet-material. contacts. the. barrier plate and engages the clamping. means. In conveying the wood veneer from the delivery position to the forward. stacking position, a circuit is broken signaling. a slowdown, in the rotational speed of the conveyor. When the sheet materialcontacts the clamping means andbarrier plate, another circuit is broken signaling: (1) retraction of the reciprocatingconveyor from. beneath the sheet material a distance greater than the width of the sheet material, allowingqthe trailinguedge thereof tofa ll by gravity to the receiving surface, (2) speedup of the rotationalspeed of the reciprocatingconveyor, and (3) withdrawal of the clamping means. so as to. release the lead edge of the sheet material. The sheet material, aligned bythe barrier plate and released at its lead and trailing edges, falls. to the receiving surface.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view with parts broken away of the stacking apparatus of thisinvention. showing a pieceof sheet materialto be stacked.

FIG. 2 is an elevational view of the apparatus along section line 2-2 of FIG. 1 showing the reciprocating conveyorvin its delivery and forward stackingpositions:

FIG. 3. isan enlarged fragmentary view along section line 3-3 of FIG. 1 showing detailsof thercamassembly for operation ofthe clamping means.

FIG. 4. is an enlarged fragmentary view along section line M of FIG. 1 showing details oftheclamping means.

FIG. is a functional schematic of thestacking apparatus of this invention;

DETAILED. DESCRIPTION OF THE INVENTION- Broadly, theapparatus of this invention comprises'a rapidly r reciprocating conveyor for conveying. sheet; material from, a

delivery position to a position overlying a receiving surface, means to align the lead edge of the veneer over the receiving surface, clamping means to hold the lead edge of the veneer, means to retract the reciprocating conveyor from beneath the sheet material and at the same time: cause withdrawal and release of the. clamping means, allowing the sheet material to fall to the receiving surface, and means to coordinate reciprocation of the conveyor with release of the sheet material by the clamping means.

The present apparatus is most useful in the production of plywood at the end of a continuous line which loads individual veneer pieces onto a moving conveyor in a particular. sequence, coats the upper surfaces of the veneer with adhesive, loads additional uncoated veneer beyond the adhesive coating station and delivers the veneer to the above apparatus of this invention where the individual veneers coated and uncoated, are stacked to form a laminated structure which is hot pressed to make pagels of plywood.

Referring to El 1, the stacking apparatus comprises rectangular frame 1 having at one end two belt conveyors (one stationary and one reciprocating) and at the other end a barrier plate or backstop having clamping means projecting therefrom. The stationary conveyor 2 is mounted above the reciprocating conveyor 3fand serves to deliver sheet material to the top surface of the reciprocating conveyor. Reciprocating. conveyor 3 is mounted for horizontal travel along suitable tracks located along. the side members of frame 1. As shown in FIG. 2, the reciprocating belt conveyor is reciprocal between a delivery position located a distance from barrier plate 8:

greater than the width of the sheet material being stacked, and a forward stacking position closely adjacent barrier plate 8 and in horizontalalignment with clamping means 20. The reciprocating belt conveyor is rapidly reciprocated between these two positions by hydraulic cylinder 4 having its cylinder attached at one end to frame 1 and its. piston attached to linkingmembers 5a and. 5b. Linking member 5a is pivotally mounted to frame 1 at one end and attached. at the other end to. linking member'Sb which is attached to the. trailing edge of reciprocal conveyor 3. The conveyor should be capableof reciprocating between its delivery. position and forward stacking position in a time period of about I second. Stationa'r.

ry belt conveyor 2 and reciprocal belt conveyor 3 are suitably.

driven'by motors 6 and 7 respectively. Motor 7 is connected to. variable transformers-for slowing the rotational speed of the belt conveyor at predetermined time intervals, as will be presently explained in connection with the schematic of FIG. 5. Both the stationary conveyor andthe reciprocal conveyor are shown as belt conveyors; however, other types of conveying devices may beused.

At the opposite end. of the stationary and reciprocal belt conveyors is located barrier plate or backstop plate8 forming an alignment surfaceto align the lead edge of sheet material delivered into contact with it by the variable speed reciprocat'. ing conveyor. The barrierplate serves, in other words, as an.

indexing pointfor the lead edge of the veneer so that all of the I veneer is evenly stacked. Adjacent to andbelow barrier plate 8 is located receivingsurface 9, most convenientlya conventionalscissors hoist or lift. on which veneer or other sheet material l0-is stacked. The scissors lift 9 includes means for lowering it as each sheet of material is delivered to its surface in amounts substantially equal. to the thickness of the sheet, thus maintaining thetop of the receiving surface at substantiallythesame level-atalltimes; Means for doing so are well known. V

Projecting through barrier plate 8. are a series of clamping means20which serve to engage and hold the lead edgerof the; sheet material delivered-into stacking position by reciprocal; belt oonveyor3'. Aligningmembers 13 attached-.to. barrier plate 8' have lower arcuate surfaces which assist in guiding the. sheet materialintothe clamping means. As shown in FIG. 2% theyarepositioned at spaced intervals adjacent the clamping: fingers so that their lower arcuate surfaces guide the sheet material between the. clamping fingers of each of thespaced' apart clamping means. Aligning members 13 are particularly advantageous when wood veneer is being processed as the thin sheets of veneer tend to buckle and warp. Details of the clamping mechanism and its operationare shown in FIGS. 3 and 4. As shown in FIG. 4, each of the clamping members comprises opposed elements 21 and 22 attached through double link members 23 and 24 and a carrier member 25 to plate 26 which is vertically slidable against barrier plate 8. As shown I in FIG. 4, the finger 21 is pivotally mounted relative to finger 22, with the two fingers being spring-biased toward each other by spring 27. The gap opening between fingers 21 and 22 and the pressure at which they are spring-loaded may be varied as desired to accommodate varying thicknesses of veneer or other sheet material. Arm member 27 is pivotally connected to carrier member 25 at one end and clamped to shaft 28 at the other. Arm member 29 is pivotally connected to linking members 23 at one end and clamped to shaft 30 at the other. Shafts 28 and 30 extend the full width of barrier plate 8 with each of the series of clamping means secured to the shafts as shown in FIG. 4. Shafts 28 and 30 are also connected at one end to a cam control mechanism whose operation will be described in detail.

FIG. 3 shows in detail the control mechanism. Shaft 28 is connected through suitable linking members 33 and 34 to eccentric 40. Shaft 30 is connected to cam follower 41 by linking arms 35 and 36. Cam 32 rotates about shaft 37, suitably connected through gearbox 38 to motor 39. Cam follower 41 rides along the surface of cam 32. The microswitch 42, positioned as shown in FIG. 3, rides along the surface of member 31 attached to cam 32 at predetermined intervals. Reference to FIGS. 3 and 4 shows that as cam 32 rotates counterclockwise, the level of point 40 drops, rotating shaft 28 counterclockwise. This causes both of the clamping mechanisms to drop to a point below their initial position as shown by the shadow lines in FIG. 4. As shown, rotation of shaft 28 moves plate 26 downwardly in straight line motion. At the same time, cam follower 41, attached to shaft 30 through linking arms 35 and 36 rides along the surface of cam 32 but remains at substantially the: same level because of the shape of the cam. When the clamping fingers have reached their lowest point as shown by the shadow lines in FIG. 4, the eccentric 40 is at its lowest position. As cam member 32 continues to rotate, cam follower 41, following the surface of cam 32, drops, rotating shaft 30 counterclockwise. Rotation of shaft 30 retracts the clamping fingers through barrier plate 8 as shown in FIG. 4 which serves to draw the veneer up firmly against the plate as it moves out of the grasp of the fingers. As cam 32 further rotates and returns to the position shown in FIG. 3, clamping fingers 21 and 22 are moved up to their initial position and back through barrier plate 8 in reverse order. The entire sequence for the series of clamping fingers spaced at intervals along barrier plate 8 (see FIG. 1) takes only about 2 seconds.

To control the coordinate movable conveyor 3 and the action of clamping means 20, a suitable control mechanism is employed. As part of the control mechanism sensing means 11, comprising a light source and detector, and sensing means 12, also comprising a light source and detectorare employed. Sensing means 11 is mounted on suitable brackets as shown in FIG. 1 and is located a predetermined distance between the delivery position and forward stacking position of reciprocal belt conveyor 3. Reciprocal conveyor 3 and stationary conveyor 2 are normally driven at about 300 feet per minute. This speed is too rapid for delivering the sheet material into engagement with the series of clamping fingers. The sheet material must therefore be slowed to a speed less than 300 feet per minute for delivery. To accomplish this, sensing means 11 is operatively connected to variable transformers also connected to motor 7 which drives belt conveyor 3. As the sheet material is delivered by conveyor 3 from the delivery position to the forward stacking position, it disrupts the light beam going between the light source and detector of sensing means 11. The belts on the conveyor are slowed from about 300 feet per minute to about 100 feet per minute, thus slowing the sheet material as it approaches barrier plate 8 and the series of clamping fingers 20.

As the sheet material is conveyed intocontact with barrier plate 8 and clamping fingers 20, it disrupts the light beam between the detector and light source of sensing means 12. Disruption of this light beam signals: (1) speedup of the belts on the moving conveyor to their initial speed of around 300 feet per minute; (2) retraction of the movable belt conveyor 3 to a position back from the barrier plate 8 a distance greater than the width of the sheet material so that the material can fall by gravity to the top of the receiving surface or scissors lift; and (3) movement of the clamping fingers as described previously and shown in FIG. 3 and 4. The clamping fingers are programmed to move straight down approximately 3 A inches, withdraw through the barrier plate 8 and return to their initial projecting position. During this motion, they draw the sheet material held in their grasp firmlyagainst barrier plate 8 and release it. Retraction of the conveyor and the motion of the clamping fingers takes place substantially simultaneously, thus allowing the veneer sheet to fall to the top of the receiving surface with the lead edge of the veneer being the indexing point.

Reference is now made to FIG. 5 for a more detailed explanation of the control mechanism. Closing switch 101 connects starter 102 of hydraulic pump motor 103 with a source of line voltage through line 104. Closing of switch 105 connects wires 106 and 107 to a source of lower voltage, such as 110 volts. When pushbutton 70 is closed, the connection to pilot light 71 and a 110-volt coil in starter 102 is completed.

This applies 440 volts to start hydraulic pump motor 103. The line 106 also connects forward pushbutton 74 and relay 70 through line 103 as well as pushbutton 76 and relay 72 through line 109.

Depression of pushbutton 78 energizes relay 60 closing contacts 60a and 60b thus completing the main circuit through line 110. This closes a circuit through line 111 containing photoelectric cell 11a, relay 62 and relay 64. By energizing line 111, photocell 11a energizes relay 62 having normally closed contacts 62a and 62b. Contacts in variable transformer 112 are thus closed and movable belt conveyor motor 7 is started (usually at a speed of 300 feet per minute). When the beam of photocell 11a is broken, relay 62 is deenergized, opening contacts 62a and 62b which in turn deenergizes the variable transformer 112. At the same time, relay 64 is energized and closes normally open contacts 64a and 64b to close contacts in variable transformer 114 which slows down movable conveyor belt motor 7 from about 300 feet per minute to 150 feet per minute.

As the veneer sheet material approaches barrier plate 8, the photoelectric beam running between the light source and detector 12 is broken. When the beam of photoelectric cell 12a in line 118 is broken, switch 119 opens and reenergizes relay 62, closing its contacts 62a and 62 b. T his deenergizes relay 64 and opens its contacts 64a and 64 b as well as opening contacts in variable transformer 114, thereby returning power to variable transformer 112 which speeds the movable carriage belt motor 7 up to its original speed of about 300 feet per minute.

Line 115 connects to variable transformer 116 and to stationary conveyor belt motor 6. The operation of this motor is controlled through start pushbutton 82 and stop pushbutton 84.

Line 118 energizes the photoelectric cell 12a which passes current through its normally open contacts 110 to relay 66 and its normally open contacts 660 to limit switch 120 which controls the directional control valve 121 on the hydraulic pump 4 which moves the movable conveyor belt carrier to full reverse. At full reverse relay 68 reverses its contacts 68a and relay 66 reverses contact 66a. The cam-mounted limit switch 120, controlling directional flow control valve 121, then moves the carriage of the movable conveyor to the forward position.

When the beam of photoelectric cell 12a is broken, contacts 119 are opened, energizing variable transformer 122 through cam-mounted limit switch 42. This starts motor 39 of the clamping mechanism. Limit switch 42 is controlled by a cam 31 mounted on the cam member 32 which, after one revolution trips suitable contacts deenergizing variable transformer 122 and stopping motor 39.

Pressing forward pushbutton 74 on wire 108 energizes relay 56 which closes its contact 56a and 56b energizing relay 66 which moves the movable belt conveyor carriage to forward position independent of the automatic cycle.

Pressing reverse pushbutton 76 on wire 109 energizes relay 58 which closes its contacts 58a and 58b energizing relay 68 which moves the movable belt conveyor carriage to reverse position independent of the automatic cycle. These two pushbuttons are provided so that the automatic control mechanism can be overridden if necessary.

Pressing of emergency stop pushbutton 80 deenergizes relay 60 and opens its contacts 60a and 60b disconnecting the 110- volt line circuit.

Pressing hydraulic pump stop pushbutton 72 deenergizes the coil in hydraulic pump starter 102 stopping the hydraulic pump motor 103 and deenergizing lines 108 and 109.

Opening of switch 101 deenergizes wire 104 connecting the source of voltage to starter 102.

The stacking apparatus described is capable of rapidly stacking veneer evenly and uninterruptedly When used for stacking wood veneer, for example, veneer sheets, coated and uncoated with adhesive, are evenly stacked. The stack of veneer is delivered to a suitable hot press for laminating the sheets of veneer into sheets of plywood.

It is believed that the invention will have been clearly understood from the foregoing detailed description of my nowpreferred illustrated embodiment. Changes in the details of construction may be resorted to without departing from the spirit of the invention and is accordingly my intention that no limitations be implied and that the hereto annexed claims be given the broadest interpretation to which the employed language fairly admits.

Iclaim:

1. A stacking apparatus for wood veneer sheets comprising:

a receiving surface for receiving sheets of veneer,

a barrier plate mounted above and adjacent to the receiving surface whereon sheets of veneer are to be stacked, the barrier plate forming an alignment surface for the leading edge of the veneer sheets delivered into a stacking position above the receiving surface,

a reciprocating conveyor having moving endless belts for supporting and moving individual sheets of veneer along the top surface thereof, the conveyor reciprocating between a retracted position overlying the receiving surface,

driving means operatively connected to the conveyor for rapidly shuttling the conveyor between the retracted and forward stacking positions,

clamping fingers projecting through the barrier plate at spaced intervals, positioned so as to engage the leading edge of the veneer sheet delivered into forward stacking position, the clamping fingers (l) engaging and clamping the leading edge of individual sheets of veneer advanced into stacking position, (2) retracting to pull the leading edge of the veneer against the alignment surface formed by the barrier plate and (3) releasing the sheet of veneer while the reciprocating conveyor is in retracted position, and

control means for coordinating action of the clamping fin gers resulting in release of the veneer sheet with movement of the reciprocating conveyor to its retracted position, to allow the aligned sheets of veneer to fall by gravity to the receiving surface.

2. The apparatus of claim 1 wherein the driving means is capable of reciprocating the conveyor between the retracted and stacking positions within a time period of about one second. 7 g p 3. The apparatus of claim 1 including means for delivering a sheet of veneer onto the surface of the reciprocating conveyor.

4. The apparatus of claim 1 including means for lowering the receiving surface as each sheet of veneer is delivered thereon an amount substantially equal to the thickness of the veneer sheet.

5. The apparatus of claim 1 wherein the control means includes first sensing means disposed at a predetermined point between the retracted position and the stacking position of the reciprocating conveyor for sensing the leading edge of the reciprocating conveyor when advancing into stacking position, and signaling slowdown of the speed of the endless belts of the reciprocating conveyor, and

second sensing means sensing when the leading edge of the veneer sheet delivered into stacking position by the reciprocating conveyor is in engagement with the clamping fingers and against the barrier plate, the second sensing means signaling retraction of the reciprocating conveyor, release of the leading edge of the sheet of veneer by the clamping fingers and speed up of the endless belts of the reciprocating conveyor.

6. The apparatus of claim 5 including cam means operatively connected to the clamping fingers programmed to move the clamping fingers engaging the leading edge of the veneer sheet downwardly a predetermined distance, retract them through the barrier plate to release the veneer sheet and align the leading edge of the veneer sheet with the alignment surface of the barrier plate, and return them to their initial position on receipt of a signal from the second sensing means.

7. The apparatus of claim 6 wherein the clamping fingers comprise a plurality of spaced-apart, spring-biased opposed elements between which the leading edge of the veneer sheet is directed.

8. A stacking apparatus for wood veneer compising:

a receiving surface for receiving sheets of veneer,

a barrier plate mounted above and adjacent to the receiving surface whereon sheets of veneer are to be stacked, the barrier plate forming an alignment surface for the leading edge of the veneer sheets delivered into a stacking position above the receiving surface,

a reciprocating conveyor having moving endless belts for supporting and moving individual sheets of veneer along the top surface thereof between a retracted position offset from the receiving surface and stacking position overlying the receiving surface,

driving means operatively connected to the conveyor for shuttling the conveyor between the retracted and stacking positions,

clamping fingers projecting through the barrier plate at spaced intervals positioned so as to engage the leading edge of the sheets of veneer delivered into stacking position, the clamping fingers (l) engaging and clamping the individual sheets of veneer advanced into stacking position by the reciprocating conveyor, and (2) retracting through the barrier plate to pull the leading edge of the veneer against the alignment surface of the barrier plate and thereby release the sheet of veneer while the reciprocating conveyor is in retracted position, allowing the aligned sheets of veneer to fall by gravity to the receiving surface,

first sensing means disposed at a predetermined point between the retracted and the forward stacking positions of the reciprocating conveyor for sensing the leading edge of the conveyor when advancing to the stacking position and signaling slowdown of the speed of the endless belts thereof, and

second sensing means sensing when the leading edge of the veneer sheet delivered into stacking position by the reciprocating conveyor is in engagement with the clamping fingers and against the barrier plate, the second sensing means signaling retraction of the reciprocating conveyor, release of the leading edge of the sheet of veneer by the clamping fingers and speed up of the endless belts of the reciprocating conveyor. 

1. A stacking apparatus for wood veneer sheets comprising: a receiving surface for receiving sheets of veneer, a barrier plate mounted above and adjacent to the receiving surface whereon sheets of veneer are to be stacked, the barrier plate forming an alignment surface for the leading edge of the veneer sheets delivered into a stacking position above the receiving surface, a reciprocating conveyor having moving endless belts for supporting and moving individual sheets of veneer along the top surface thereof, the conveyor reciprocating between a retracted position overlying the receiving surface, driving means operatively connected to the conveyor for rapidly shuttling the conveyor between the retracted and forward stacking positions, clamping fingers projecting through the barrier plate at spaced intervals, positioned so as to engage the leading edge of the veneer sheet delivered into forward stacking position, the clamping fingers (1) engaging and clamping the leading edge of individual sheets of veneer advanced into stacking position, (2) retracting to pull the leading edge of the veneer against the alignment surface formed by the barrier plate and (3) releasing the sheet of veneer while the reciprocating conveyor is in retracted position, and control means for coordinating action of the clamping fingers resulting in release of the veneer sheet with movement of the reciprocating conveyor to its retracted position, to allow the aligned sheets of veneer to fall by gravity to the receiving surface.
 2. The apparatus of claim 1 wherein the driving means is capable of reciprocating the conveyor between the retracted and stacking positions within a time period of about one second.
 3. The apparatus of claim 1 including means for delivering a sheet of veneer onto the surface of the reciprocating conveyor.
 4. The apparatus of claim 1 including means for lowering the receiving surface as each sheet of veneer is delivered thereon an amount substantially equal to the thickness of the veneer sheet.
 5. The apparatus of claim 1 wherein the control means includes first sensing means disposed at a predetermined point between the retracted position and the stacking position of the reciprocating conveyor for sensing the leading edge of the reciprocating conveyor when advancing into stacking position, and signaling slowdown of the speed of the endless belts of the reciprocating conveyor, and second sensing means sensing when the leading edge of the veneer sheet delivered into stacking position by the reciprocating conveyor is in engagement with the clamping fingers and against the barrier plate, the second sensing means signaling retraction of the reciprocating conveyor, release of the leading edge of the sheet of veneer by the clamping fingers and speed up of the endless belts of the reciprocating conveyor.
 6. The apparatus of claim 5 including cam means operatively connected to the clamping fingers programmed to move the clamping fingers engaging the leading edge of the veneer sheet downwardly a predetermined distance, retract them through the barrier plate to release the veneer sHeet and align the leading edge of the veneer sheet with the alignment surface of the barrier plate, and return them to their initial position on receipt of a signal from the second sensing means.
 7. The apparatus of claim 6 wherein the clamping fingers comprise a plurality of spaced-apart, spring-biased opposed elements between which the leading edge of the veneer sheet is directed.
 8. A stacking apparatus for wood veneer compising: a receiving surface for receiving sheets of veneer, a barrier plate mounted above and adjacent to the receiving surface whereon sheets of veneer are to be stacked, the barrier plate forming an alignment surface for the leading edge of the veneer sheets delivered into a stacking position above the receiving surface, a reciprocating conveyor having moving endless belts for supporting and moving individual sheets of veneer along the top surface thereof between a retracted position offset from the receiving surface and stacking position overlying the receiving surface, driving means operatively connected to the conveyor for shuttling the conveyor between the retracted and stacking positions, clamping fingers projecting through the barrier plate at spaced intervals positioned so as to engage the leading edge of the sheets of veneer delivered into stacking position, the clamping fingers (1) engaging and clamping the individual sheets of veneer advanced into stacking position by the reciprocating conveyor, and (2) retracting through the barrier plate to pull the leading edge of the veneer against the alignment surface of the barrier plate and thereby release the sheet of veneer while the reciprocating conveyor is in retracted position, allowing the aligned sheets of veneer to fall by gravity to the receiving surface, first sensing means disposed at a predetermined point between the retracted and the forward stacking positions of the reciprocating conveyor for sensing the leading edge of the conveyor when advancing to the stacking position and signaling slowdown of the speed of the endless belts thereof, and second sensing means sensing when the leading edge of the veneer sheet delivered into stacking position by the reciprocating conveyor is in engagement with the clamping fingers and against the barrier plate, the second sensing means signaling retraction of the reciprocating conveyor, release of the leading edge of the sheet of veneer by the clamping fingers and speed up of the endless belts of the reciprocating conveyor. 